Interpretive Summary: Restoration practitioners often attempt to restore damaged rangelands by using indigenous genotypes. However, this is problematic because traditional ecosystems are disappearing, in part because of invasion by weedy species that disrupt ecosystem function. We contend that designing plant materials with specific functional traits can overcome the challenges to restoring ecosystem function. Plant populations that display appropriate levels and diversity for functional traits may interact to form viable communities that are more stable and resilient in the face of invasive plants. Ecological niches are increasingly likely to be occupied by desirable perennial species over time, rather than by the invasive plants that characterize ecosystem dysfunction. Altered ecological processes include priority effects of aggressive species, competitive interference, and positive feedbacks that exacerbate weedy dominance. An improved understanding of trade-offs among physiological traits, growth under low-nutrient conditions, and seedling establishment will identify functional traits that can be manipulated to generate plant materials via "assisted evolution" that will be more effective in fostering self-regenerating processes in the modified environments that increasingly occupy our planet.

Technical Abstract:
Ecologists worldwide recognize that the novel ecosystems of the future will display radically different structure and function from ecosystems that have dominated the study of ecology up until the prsent time. Because of both abiotic and biotic obstacles, rangelands dominated by invasive plants are among the most difficult lands to repair. Here, we make the case for designed plant materials using a conceptual framework that is anchored by functional traits that may overcome specific obstacles associated with annual-grass invasion. We argue herein that plant performance trumps indigenous genotypes in the case of modified ecosystems. Nevertheless, we emphasize that indigenous genotypes may contribute to the solution when combined with applicable ecological and physiological principles.